I have 3 licenses.
One of the computers had a fried motherboard, was trashed and was replaced with a new Dell.
I am unable to activate em Client on the new machine.
Unfortunately you need to deactivate a license before moving it to another computer. As the motherboard is fried and you cannot do this, there are a few options you can try.
If you have a Free License, either register a new license using a different email address, or write to eM Client and ask them to deactivate the existing license for you. If you have a Pro License, you can deactivate it yourself using the License Manager.